Let's talk about the Analog VU Meter Bridge. I decided to make the Meter Bridge separate from the mixer, because of limited space inside my Ham Radio room. I am placing the unit right above my computer monitor and Digital Clocks.
This board is designed to accept the Mixer Buss output and drive Analog VU Meters along with a PEAK LED indicator.
A SIMPLE EXPANATION
The audio enters the board via J-1 and is fed to an LM5532 OP AMP. The OP Amp feeds a full wave rectifier to convert it to a low voltage that feeds the VU Meter. The signal then continues to an LM339 Quad Differential Comparator that drives the LED Peak indicator.
MORE DETAILED
Integrated circuit U2A, diodes Dl thru D4 and the associated resistors convert the balanced left program channel output to a floating D.C. voltage to drive the left program VU meter. Therefore, the effects of loading the console output or erroneously grounding one of the console outputs will be reflected on the VU meter. Trimmer VR2 provides “0” VU adjustment for a range of console outputs. differential amplifier U2B converts the meter voltage from floating to single ended prior to applying the voltage to U15A. Integrated circuit U15A functions as a peak detector with the trip point adjusted by VR12.
When the positive peak of the audio signal (applied to U15 pin 4) becomes more positive than the reference set by VR12 the output of U15A will go to -15 volts and in turn the output of U15B will go to -15 volts and illuminate the peak LED. At the conclusion of the peak U15 pin 4 will fall to lower potential than the reference set by VR12, and the output of U15A (which is an open collector) will allow C59 to be charged by R115. When the potential at U15 pin 9 is more positive than the reference at U15 pin 8 the output of U15 B will go high, and the LED will extinguish. Capacitor C59 and resistor R115 act as a .5 second peak stretcher which allows the LED to properly illuminate.
The meters I used are 'surplus' RADIO SYSTEMS meters, that I pulled from a large 24 channel mixer I bought for spare parts.
The unit will also reduce my parts count on the Output Board.
So, let's get to it.
Here is the schematic: 
MONO AND POWER
And the designed circuit board:
Sorry for the crappy photo.
After building the prototype, I decided putting the trim POTS on the bottom of the board made drawing the traces more difficult. So, I placed the 'peak' controls closer to the IC they are connected to. I can slide the board out to get to them. You will see that when we make the cabinet. (I am hoping the settings are a 'set and forget' type.)
I used the meters from the Original Meter Bridge I built around 2008. I removed it from the cabinet and placed it on a shelf until I get the rest of it completed.
Here is the original cabinet that sat on top of my original mixer.
CAPACITOR DISC C-001 0.1
CAPACITOR DISC C-002 0.1
CAPACITOR DISC C-003 0.1
CAPACITOR DISC C-004 0.1
CAPACITOR DISC C-005 0.1
CAPACITOR DISC C-006 0.1
CAPACITOR DISC C-007 0.1
CAPACITOR DISC C-008 0.1
CAPACITOR DISC C-009 0.1
CAPACITOR DISC C-010 0.1
CAPACITOR DISC C-030 0.1
CAPACITOR DISC C-058 0.1
CAPACITOR DISC C-059 0.1
CAPACITOR DISC C-060 0.1
CAPACITOR DISC C-062 0.1
CAPACITOR DISC C-202 0.1
CAPACITOR DISC C-203 0.1
CAPACITOR DISC C-206 0.1
CAPACITOR DISC C-207 0.1
RESISTOR FILM R-102 1.8 K ¼ W 1%
RESISTOR FILM R-110 1.8 K ¼ W 1%
RESISTOR FILM R-111 1.8 K ¼ W 1%
RESISTOR FILM R-112 1.8 K ¼ W 1%
RESISTOR FILM R-113 1.8 K ¼ W 1%
POTENTIOMETER TRIM RV-002 10 K
POTENTIOMETER TRIM RV-003 10 K
POTENTIOMETER TRIM RV-004 10 K
POTENTIOMETER TRIM RV-005 10 K
POTENTIOMETER TRIM RV-006 10 K
POTENTIOMETER TRIM RV-012 10 K
POTENTIOMETER TRIM RV-013 10 K
POTENTIOMETER TRIM RV-014 10 K
POTENTIOMETER TRIM RV-015 10 K
POTENTIOMETER TRIM RV-016 10 K
CAPACITOR FILM C-016 10 PF
CAPACITOR FILM C-017 10 PF
CAPACITOR FILM C-019 10 PF
CAPACITOR FILM C-020 10 PF
CAPACITOR FILM C-022 10 PF
CAPACITOR FILM C-023 10 PF
CAPACITOR FILM C-025 10 PF
CAPACITOR FILM C-026 10 PF
CAPACITOR FILM C-028 10 PF
CAPACITOR FILM C-029 10 PF
RESISTOR FILM R-012 10.2 K ¼ W 1%
RESISTOR FILM R-013 10.2 K ¼ W 1%
RESISTOR FILM R-017 10.2 K ¼ W 1%
RESISTOR FILM R-018 10.2 K ¼ W 1%
RESISTOR FILM R-019 10.2 K ¼ W 1%
RESISTOR FILM R-020 10.2 K ¼ W 1%
RESISTOR FILM R-021 10.2 K ¼ W 1%
RESISTOR FILM R-023 10.2 K ¼ W 1%
RESISTOR FILM R-024 10.2 K ¼ W 1%
RESISTOR FILM R-028 10.2 K ¼ W 1%
RESISTOR FILM R-029 10.2 K ¼ W 1%
RESISTOR FILM R-030 10.2 K ¼ W 1%
RESISTOR FILM R-031 10.2 K ¼ W 1%
RESISTOR FILM R-032 10.2 K ¼ W 1%
RESISTOR FILM R-034 10.2 K ¼ W 1%
RESISTOR FILM R-035 10.2 K ¼ W 1%
RESISTOR FILM R-039 10.2 K ¼ W 1%
RESISTOR FILM R-040 10.2 K ¼ W 1%
RESISTOR FILM R-041 10.2 K ¼ W 1%
RESISTOR FILM R-042 10.2 K ¼ W 1%
RESISTOR FILM R-043 10.2 K ¼ W 1%
RESISTOR FILM R-045 10.2 K ¼ W 1%
RESISTOR FILM R-046 10.2 K ¼ W 1%
RESISTOR FILM R-050 10.2 K ¼ W 1%
RESISTOR FILM R-051 10.2 K ¼ W 1%
RESISTOR FILM R-052 10.2 K ¼ W 1%
RESISTOR FILM R-053 10.2 K ¼ W 1%
RESISTOR FILM R-054 10.2 K ¼ W 1%
RESISTOR FILM R-056 10.2 K ¼ W 1%
RESISTOR FILM R-057 10.2 K ¼ W 1%
RESISTOR FILM R-061 10.2 K ¼ W 1%
RESISTOR FILM R-062 10.2 K ¼ W 1%
RESISTOR FILM R-063 10.2 K ¼ W 1%
RESISTOR FILM R-064 10.2 K ¼ W 1%
RESISTOR FILM R-065 10.2 K ¼ W 1%
RESISTOR FILM R-016 100 K ¼ W 1%
RESISTOR FILM R-027 100 K ¼ W 1%
RESISTOR FILM R-038 100 K ¼ W 1%
RESISTOR FILM R-049 100 K ¼ W 1%
RESISTOR FILM R-060 100 K ¼ W 1%
RESISTOR FILM R-011 110 ¼ W 1%
RESISTOR FILM R-022 110 ¼ W 1%
RESISTOR FILM R-033 110 ¼ W 1%
RESISTOR FILM R-044 110 ¼ W 1%
RESISTOR FILM R-055 110 ¼ W 1%
SOCKET I.C. U-011S 14 PIN DIP
SOCKET I.C. U-015S 14 PIN DIP
SOCKET I.C. U-016S 14 PIN DIP
DIODE GERMANIUM D-001 1N270
DIODE GERMANIUM D-002 1N270
DIODE GERMANIUM D-003 1N270
DIODE GERMANIUM D-004 1N270
DIODE GERMANIUM D-005 1N270
DIODE GERMANIUM D-006 1N270
DIODE GERMANIUM D-007 1N270
DIODE GERMANIUM D-008 1N270
DIODE GERMANIUM D-009 1N270
DIODE GERMANIUM D-010 1N270
DIODE GERMANIUM D-011 1N270
DIODE GERMANIUM D-012 1N270
DIODE GERMANIUM D-013 1N270
DIODE GERMANIUM D-014 1N270
DIODE GERMANIUM D-015 1N270
DIODE GERMANIUM D-016 1N270
DIODE GERMANIUM D-017 1N270
DIODE GERMANIUM D-018 1N270
DIODE GERMANIUM D-019 1N270
DIODE GERMANIUM D-020 1N270
RESISTOR FILM R-014 20 K ¼ W 1%
RESISTOR FILM R-015 20 K ¼ W 1%
RESISTOR FILM R-025 20 K ¼ W 1%
RESISTOR FILM R-026 20 K ¼ W 1%
RESISTOR FILM R-036 20 K ¼ W 1%
RESISTOR FILM R-037 20 K ¼ W 1%
RESISTOR FILM R-047 20 K ¼ W 1%
RESISTOR FILM R-048 20 K ¼ W 1%
RESISTOR FILM R-058 20 K ¼ W 1%
RESISTOR FILM R-059 20 K ¼ W 1%
CAPACITOR ELECTROLYTIC C-201 220 UF @ 50 V
CAPACITOR ELECTROLYTIC C-204 220 UF @ 50 V
CAPACITOR ELECTROLYTIC C-205 220 UF @ 50 V
CAPACITOR ELECTROLYTIC C-208 220 UF @ 50 V
CONNECTOR IDC J-001 2X7 ODD/EVEN
RESISTOR FILM D-201 330 ½ W 1%
RESISTOR FILM R-200 330 ½ W 1%
RESISTOR FILM R-202 330 ½ W 1%
RESISTOR FILM R-203 330 ½ W 1%
RESISTOR FILM R-114 4.7 MEG ¼ W 1%
RESISTOR FILM R-115 4.7 MEG ¼ W 1%
RESISTOR FILM R-116 4.7 MEG ¼ W 1%
RESISTOR FILM R-117 4.7 MEG ¼ W 1%
RESISTOR FILM R-118 4.7 MEG ¼ W 1%
CONNECTOR MOLEX .1 J-001 7 PIN .1
CONNECTOR MOLEX .1 J-400 7 PIN .1
SOCKET I.C. U-002S 8 PIN DIP
SOCKET I.C. U-003S 8 PIN DIP
SOCKET I.C. U-004S 8 PIN DIP
SOCKET I.C. U-005S 8 PIN DIP
SOCKET I.C. U-006S 8 PIN DIP
LED 5MM D-201 GREEN LED
LED 5MM D-202 GREEN LED
LED 5MM D-203 GREEN LED
LED 5MM D-204 GREEN LED
I.C. COMPARATOR U-015 LM339
I.C. COMPARATOR U-016 LM339
I.C. COMPARATOR U-017 LM339
I.C. OP AMP U-002 NE5532
I.C. OP AMP U-003 NE5532
I.C. OP AMP U-004 NE5532
I.C. OP AMP U-005 NE5532
I.C. OP AMP U-006 NE5532
METER VU TYPE VU-001
METER VU TYPE VU-002
METER VU TYPE VU-003
METER VU TYPE VU-004
METER VU TYPE VU-005
BOARD JLC PRO
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Now we order the boards and wait.
(Insert Jeopardy Theme song here)
OK, here is the new board.
Let's start stuffing the board with parts.
Here is the board with a few components installed.
The schematic calls for the rectifier diodes to be 1n270. These get a bit pricey ($1.50 each) if you do a one channel mockup, then a full proto board, and a final board.
So, I tried the less expensive 1n34a Germanium diodes ($.30), and they worked just as well as the 1n270. Feel free to use either unit.
(NOTE: Prices may vary, but you get the idea.)
I started with the power input circuits and made sure it worked. I then moved onto Left Program circuit. I wired it up to the Peak circuit. The meter circuit worked well, so I moved onto the PEAK circuit.
You get the idea. Do this one channel at a time, verifying the circuits as you go.
Continue on.
And here it is, the completed and working VU Meter Board.
Before we move onto a cabinet, I would like to re-visit the LED Meters that I was working on. I have had a hell of a time getting these to work properly but I may want to put the LED and the ANALOG Meters in the same cabinet.
So, we will set this aside, get the LED version to work, then do a separate blog on the cabinet.
See you then!!!
